The utility model provides a pneumatic beam transport trailer suitable for both a single-track beam and a double-track beam and capable of passing a limited space, which belongs to the bridge machinery field. The beam transport trailer adopts a four-main-beam structure composed of two external main beams and two internal main beams which are symmetrical to one another. The bottoms of the external main beams and the internal main beams are provided with a sideslip slide way made of an L-shaped steel pair. A flange slide block serving both as a slide block and as a connecting piece is equipped inside the slide way in a matching way. The flange slide block can be independently connected with a wheel assembly and drive the wheel assembly to move inside the slide way among the external main beams and the internal main beams. Meanwhile, the flange slide block can make the connected wheel assembly fixedly connected on the lower part of a selected external main beam or a selected internal main beam so as to achieve a variable distance. The relative height of the two internal main beams is smaller than that of the two external main beams. By settling a beam-carrying dolly on the lower internal main beam track, the beam transport trailer in the utility model has self height reduced. The beam transport trailer is thus enabled to be freely adapted to single-track beams and double-track beams with high efficiency. The beam transport trailer also meets the conveying requirements of passing a limited space.